前言

專案中遇到需求，需要將多個excel的sheet合併到一個excel裡面。網上看了一下文章，但是很多都是斷章取義，不是程式碼不全，就是jar包版本不同一，為此自己解決這個問題後，把解決方案記錄下來，供後來的童鞋參考：

第一步：匯入poi相關jar包

 <dependency>
         <groupId>org.apache.poi</groupId>
         <artifactId>poi-ooxml</artifactId>
         <version>4.1.2</version
 
>
</dependency>

第二步：複製工具類

import org.apache.poi.ss.usermodel.CellType;
import org.apache.poi.ss.usermodel.DateUtil;
import org.apache.poi.ss.util.CellRangeAddress;
import org.apache.poi.xssf.usermodel.*;

import java.io.*;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;

 
/**
 * @description: 多個Excel合併Sheet
 * @author: wyj
 * @time: 2020/9/18 15:28
 */
public class ExcelUtil {

    public static void main(String[] args) {
        List<String> list = Arrays.asList(
                new File("D:\\test\\a.xlsx").toString(),
                new File("D:\\test\\b.xlsx").toString(),
                
 
new File("D:\\test\\c.xlsx").toString()
                );

        mergexcel(list,"楊洪-家庭貸-20190908(報告).xlsx","D:\\test");
        System.out.println("OJBK");
    }

    /**
     * * 合併多個ExcelSheet
     *
     * @param files 檔案字串(file.toString)集合,按順序進行合併，合併的Excel中Sheet名稱不可重複
     * @param excelName 合併後Excel名稱(包含字尾.xslx)
     * @param dirPath 儲存目錄
     * @return
     * @Date: 2020/9/18 15:31
     */
    public static void mergexcel(List<String> files, String excelName, String dirPath) {
        XSSFWorkbook newExcelCreat = new XSSFWorkbook();
        // 遍歷每個源excel檔案，TmpList為原始檔的名稱集合
        for (String fromExcelName : files) {
            try (InputStream in = new FileInputStream(fromExcelName)) {
                XSSFWorkbook fromExcel = new XSSFWorkbook(in);
                int length = fromExcel.getNumberOfSheets();
                if (length <= 1) {       //長度為1時
                    XSSFSheet oldSheet = fromExcel.getSheetAt(0);
                    XSSFSheet newSheet = newExcelCreat.createSheet(oldSheet.getSheetName());
                    copySheet(newExcelCreat, oldSheet, newSheet);
                } else {
                    for (int i = 0; i < length; i++) {// 遍歷每個sheet
                        XSSFSheet oldSheet = fromExcel.getSheetAt(i);
                        XSSFSheet newSheet = newExcelCreat.createSheet(oldSheet.getSheetName());
                        copySheet(newExcelCreat, oldSheet, newSheet);
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        // 定義新生成的xlxs表格檔案
        String allFileName = dirPath + File.separator + excelName;
        try (FileOutputStream fileOut = new FileOutputStream(allFileName)) {
            newExcelCreat.write(fileOut);
            fileOut.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                newExcelCreat.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 合併單元格
     *
     * @param fromSheet
     * @param toSheet
     */
    private static void mergeSheetAllRegion(XSSFSheet fromSheet, XSSFSheet toSheet) {
        int num = fromSheet.getNumMergedRegions();
        CellRangeAddress cellR = null;
        for (int i = 0; i < num; i++) {
            cellR = fromSheet.getMergedRegion(i);
            toSheet.addMergedRegion(cellR);
        }
    }

    /**
     * 複製單元格
     *
     * @param wb
     * @param fromCell
     * @param toCell
     */
    private static void copyCell(XSSFWorkbook wb, XSSFCell fromCell, XSSFCell toCell) {
        XSSFCellStyle newstyle = wb.createCellStyle();
        // 複製單元格樣式
        newstyle.cloneStyleFrom(fromCell.getCellStyle());
        // 樣式
        toCell.setCellStyle(newstyle);
        if (fromCell.getCellComment() != null) {
            toCell.setCellComment(fromCell.getCellComment());
        }
        // 不同資料型別處理
        CellType fromCellType = fromCell.getCellType();
        toCell.setCellType(fromCellType);
        if (fromCellType == CellType.NUMERIC) {
            if (DateUtil.isCellDateFormatted(fromCell)) {
                toCell.setCellValue(fromCell.getDateCellValue());
            } else {
                toCell.setCellValue(fromCell.getNumericCellValue());
            }
        } else if (fromCellType == CellType.STRING) {
            toCell.setCellValue(fromCell.getRichStringCellValue());
        } else if (fromCellType == CellType.BLANK) {
            // nothing21
        } else if (fromCellType == CellType.BOOLEAN) {
            toCell.setCellValue(fromCell.getBooleanCellValue());
        } else if (fromCellType == CellType.ERROR) {
            toCell.setCellErrorValue(fromCell.getErrorCellValue());
        } else if (fromCellType == CellType.FORMULA) {
            toCell.setCellFormula(fromCell.getCellFormula());
        } else {
            // nothing29
        }
    }

    /**
     * 行復制功能
     *
     * @param wb
     * @param oldRow
     * @param toRow
     */
    private static void copyRow(XSSFWorkbook wb, XSSFRow oldRow, XSSFRow toRow) {
        toRow.setHeight(oldRow.getHeight());
        for (Iterator cellIt = oldRow.cellIterator(); cellIt.hasNext(); ) {
            XSSFCell tmpCell = (XSSFCell) cellIt.next();
            XSSFCell newCell = toRow.createCell(tmpCell.getColumnIndex());
            copyCell(wb, tmpCell, newCell);
        }
    }

    /**
     * Sheet複製
     *
     * @param wb
     * @param fromSheet
     * @param toSheet
     */
    private static void copySheet(XSSFWorkbook wb, XSSFSheet fromSheet, XSSFSheet toSheet) {
        mergeSheetAllRegion(fromSheet, toSheet);
        // 設定列寬
        int length = fromSheet.getRow(fromSheet.getFirstRowNum()).getLastCellNum();
        for (int i = 0; i <= length; i++) {
            toSheet.setColumnWidth(i, fromSheet.getColumnWidth(i));
        }
        for (Iterator rowIt = fromSheet.rowIterator(); rowIt.hasNext(); ) {
            XSSFRow oldRow = (XSSFRow) rowIt.next();
            XSSFRow newRow = toSheet.createRow(oldRow.getRowNum());
            copyRow(wb, oldRow, newRow);
        }
    }
}

附加：提供一個建立空白excel的方法

 /**
     * *建立空的excel檔案,可自定義sheet名稱
     *
     * @param filePath  檔案路徑
     * @param sheetList  sheet名稱集合(名稱不可重複)
     * @return
     * @Date: 2020/9/21 17:36
     */
    public static void createBlankExcel(String filePath, List<String> sheetList) {
        try (FileOutputStream out = new FileOutputStream(new File(filePath))) {
            XSSFWorkbook workbook = new XSSFWorkbook();
            if (sheetList != null && sheetList.size() > 0) {
                for (String sheet : sheetList) {
                    workbook.createSheet(sheet);
                }
            } else {
                // 預設3個sheet
                workbook.createSheet("sheet1");
                workbook.createSheet("sheet2");
                workbook.createSheet("sheet3");
            }
            XSSFCellStyle cellStyle = workbook.createCellStyle();
            XSSFFont font = workbook.createFont();
            font.setColor(Font.COLOR_RED);
            cellStyle.setFont(font);
            workbook.write(out);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }